This invention relates to electrostatographic copiers and printers, and more particularly to a compact and less expensive development apparatus therein for producing high quality toner developed images.
In such a copier or printer, especially one for producing high-resolution images, a development apparatus, of the type including a magnetic development roller, utilizes very fine toner particles that are contained in a magnetic developer material. The developer material is carried, at a desired velocity, by the magnetic development roller for developing electrostatic latent images on an image-bearing member. Such developer material consists, for example, of a mixture of ferromagnetic carrier particles and such toner particles, at a desired concentration. The concentration or level of toner particles in the mix, as expected, is usually depleted each time an image is developed.
Ordinarily, such depletion will result in poor quality development of subsequently produced images. Therefore to ensure quality development of such subsequently developed images, the depleted spent developer must, for example, be effectively removed from each portion of the development roller, before such portion again carries fresh developer (of the desired concentration) for development.
Conventional devices for skiving or removing spent developer from the surface of development rollers are disclosed, for example, in U.S. Pat. Nos. 2,975,758; 4,660,504 and 3,982,498. These devices include, respectively, an eccentric shell about a magnetic development roller, a mechanical skive, and a magnetic brush roll.
The eccentric shell type device operates by directing the spent developer further and further away from the magnetic influence of the magnetic core of the development roller until the spent developer passively falls off gravitationally from the surface of such shell. Ordinarily, the effectiveness of such eccentric shell devices is limited because the spent developer is removed passively, and because there is a contradictory and competing need on the other hand for the same surface of the eccentric shell to be within the magnetic influence of its magnetic core so as to enable the development roller to magnetically attract fresh developer thereto from an adjacent developer feed roller.
Mechanical skive devices are often also ineffective. They typically include a mechanical edge located in skiving or scraping engagement with the developer-carrying outside surface of a development roller shell, for scraping spent developer therefrom. The spent developer so scraped off is thereafter allowed to gravitationally fall off the mechanical skive. Such mechanical skives, however, are particularly ineffective in development apparatus which utilize very fine toner particles for high resolution image development. In such development apparatus, the shell and the core of the development roller normally are being rotated in the same direction such that the net forward velocity of the spent developer is imparted by the shell. Such a net velocity, of course, will be opposite in direction to the component velocity being imparted by the magnetic core of such development roller.
The mechanical skive is particularly ineffective here because when the spent developer is still within the magnetic influence of the core of the development roller, and loses its shell-imparted forward velocity due to being scraped or skived from such shell, the magnetic tendency of the core will be to move the spent developer backwards away from the mechanical skive. The results often are undesirable bridging, and flaking of the toner component of such developer.
On the other hand, although it is well known to use a magnetic device such as a development roller or magnetic brush roll to move developer-containing magnetic carrier particles, the effectiveness of such a roll, when used as a skive for a magnetic development roller, is significantly limited if it must work against, and must overcome the magnetic influence of the magnetic core of the development roller in order to remove spent developer from such development roller. Furthermore, because such rolls normally include a driven shell and hence separate drive means, the tendency is for them to be bulky and expensive.